Has it been confirmed that the ATP magazine baseplate can be swapped for the Magpul FPG baseplate with proper fit?
And if so are the Magpul FPG base plates same as M series baseplates as in same dimensions? Thx

Just to support niko_gpsy, I have tried the M-series mags, ATP mags, M-series extended mags, AABB extended mags, and FPG mags in my FPG.

All the extended 49~rd magazines will work no problem, the only issue is that you cannot use the "+2" style base plates and fold the gun. The original M-series and Magpul FPG base plates will fold into the receiver nicely.

As for the standard 23rd magazines, the M-series and ATP mags both fit and function properly. However, neither the M-series original base plates (the ones with the hole for gas charging) nor the "+2" style base plates will work. They just don't clear the very bottom of the pistol grip, so the magazine will not lock into place. I supposed you could sand the mag well from the inside, but I wouldn't. If you want to use 23rd magazines, you should purchase the Magpul FPG base plates or just use no base plates at all.